pam.conf

PAM.CONF(5)                     Linux-PAM Manual                     PAM.CONF(5)



NAME
       pam.conf, pam.d - PAM configuration files

DESCRIPTION
       When a PAM aware privilege granting application is started, it activates
       its attachment to the PAM-API. This activation performs a number of
       tasks, the most important being the reading of the configuration file(s):
       /etc/pam.conf. Alternatively, this may be the contents of the /etc/pam.d/
       directory. The presence of this directory will cause Linux-PAM to ignore
       /etc/pam.conf.

       These files list the PAMs that will do the authentication tasks required
       by this service, and the appropriate behavior of the PAM-API in the event
       that individual PAMs fail.

       The syntax of the /etc/pam.conf configuration file is as follows. The
       file is made up of a list of rules, each rule is typically placed on a
       single line, but may be extended with an escaped end of line: `\<LF>'.
       Comments are preceded with `#' marks and extend to the next end of line.

       The format of each rule is a space separated collection of tokens, the
       first three being case-insensitive:

        service type control module-path module-arguments

       The syntax of files contained in the /etc/pam.d/ directory, are identical
       except for the absence of any service field. In this case, the service is
       the name of the file in the /etc/pam.d/ directory. This filename must be
       in lower case.

       An important feature of PAM, is that a number of rules may be stacked to
       combine the services of a number of PAMs for a given authentication task.

       The service is typically the familiar name of the corresponding
       application: login and su are good examples. The service-name, other, is
       reserved for giving default rules. Only lines that mention the current
       service (or in the absence of such, the other entries) will be associated
       with the given service-application.

       The type is the management group that the rule corresponds to. It is used
       to specify which of the management groups the subsequent module is to be
       associated with. Valid entries are:

       account
           this module type performs non-authentication based account
           management. It is typically used to restrict/permit access to a
           service based on the time of day, currently available system
           resources (maximum number of users) or perhaps the location of the
           applicant user -- 'root' login only on the console.

       auth
           this module type provides two aspects of authenticating the user.
           Firstly, it establishes that the user is who they claim to be, by
           instructing the application to prompt the user for a password or
           other means of identification. Secondly, the module can grant group
           membership or other privileges through its credential granting
           properties.

       password
           this module type is required for updating the authentication token
           associated with the user. Typically, there is one module for each
           'challenge/response' based authentication (auth) type.

       session
           this module type is associated with doing things that need to be done
           for the user before/after they can be given service. Such things
           include the logging of information concerning the opening/closing of
           some data exchange with a user, mounting directories, etc.

       If the type value from the list above is prepended with a - character the
       PAM library will not log to the system log if it is not possible to load
       the module because it is missing in the system. This can be useful
       especially for modules which are not always installed on the system and
       are not required for correct authentication and authorization of the
       login session.

       The third field, control, indicates the behavior of the PAM-API should
       the module fail to succeed in its authentication task. There are two
       types of syntax for this control field: the simple one has a single
       simple keyword; the more complicated one involves a square-bracketed
       selection of value=action pairs.

       For the simple (historical) syntax valid control values are:

       required
           failure of such a PAM will ultimately lead to the PAM-API returning
           failure but only after the remaining stacked modules (for this
           service and type) have been invoked.

       requisite
           like required, however, in the case that such a module returns a
           failure, control is directly returned to the application or to the
           superior PAM stack. The return value is that associated with the
           first required or requisite module to fail. Note, this flag can be
           used to protect against the possibility of a user getting the
           opportunity to enter a password over an unsafe medium. It is
           conceivable that such behavior might inform an attacker of valid
           accounts on a system. This possibility should be weighed against the
           not insignificant concerns of exposing a sensitive password in a
           hostile environment.

       sufficient
           if such a module succeeds and no prior required module has failed the
           PAM framework returns success to the application or to the superior
           PAM stack immediately without calling any further modules in the
           stack. A failure of a sufficient module is ignored and processing of
           the PAM module stack continues unaffected.

       optional
           the success or failure of this module is only important if it is the
           only module in the stack associated with this service+type.

       include
           include all lines of given type from the configuration file specified
           as an argument to this control.

       substack
           include all lines of given type from the configuration file specified
           as an argument to this control. This differs from include in that
           evaluation of the done and die actions in a substack does not cause
           skipping the rest of the complete module stack, but only of the
           substack. Jumps in a substack also can not make evaluation jump out
           of it, and the whole substack is counted as one module when the jump
           is done in a parent stack. The reset action will reset the state of a
           module stack to the state it was in as of beginning of the substack
           evaluation.

       For the more complicated syntax valid control values have the following
       form:

                 [value1=action1 value2=action2 ...]


       Where valueN corresponds to the return code from the function invoked in
       the module for which the line is defined. It is selected from one of
       these: success, open_err, symbol_err, service_err, system_err, buf_err,
       perm_denied, auth_err, cred_insufficient, authinfo_unavail, user_unknown,
       maxtries, new_authtok_reqd, acct_expired, session_err, cred_unavail,
       cred_expired, cred_err, no_module_data, conv_err, authtok_err,
       authtok_recover_err, authtok_lock_busy, authtok_disable_aging, try_again,
       ignore, abort, authtok_expired, module_unknown, bad_item, conv_again,
       incomplete, and default.

       The last of these, default, implies 'all valueN's not mentioned
       explicitly. Note, the full list of PAM errors is available in
       /usr/include/security/_pam_types.h. The actionN can take one of the
       following forms:

       ignore
           when used with a stack of modules, the module's return status will
           not contribute to the return code the application obtains.

       bad
           this action indicates that the return code should be thought of as
           indicative of the module failing. If this module is the first in the
           stack to fail, its status value will be used for that of the whole
           stack.

       die
           equivalent to bad with the side effect of terminating the module
           stack and PAM immediately returning to the application.

       ok
           this tells PAM that the administrator thinks this return code should
           contribute directly to the return code of the full stack of modules.
           In other words, if the former state of the stack would lead to a
           return of PAM_SUCCESS, the module's return code will override this
           value. Note, if the former state of the stack holds some value that
           is indicative of a modules failure, this 'ok' value will not be used
           to override that value.

       done
           equivalent to ok with the side effect of terminating the module stack
           and PAM immediately returning to the application.

       N (an unsigned integer)
           jump over the next N modules in the stack. Note that N equal to 0 is
           not allowed, it would be treated as ignore in such case. The side
           effect depends on the PAM function call: for pam_authenticate,
           pam_acct_mgmt, pam_chauthtok, and pam_open_session it is ignore; for
           pam_setcred and pam_close_session it is one of ignore, ok, or bad
           depending on the module's return value.

       reset
           clear all memory of the state of the module stack and start again
           with the next stacked module.

       Each of the four keywords: required; requisite; sufficient; and optional,
       have an equivalent expression in terms of the [...] syntax. They are as
       follows:

       required
           [success=ok new_authtok_reqd=ok ignore=ignore default=bad]

       requisite
           [success=ok new_authtok_reqd=ok ignore=ignore default=die]

       sufficient
           [success=done new_authtok_reqd=done default=ignore]

       optional
           [success=ok new_authtok_reqd=ok default=ignore]

       module-path is either the full filename of the PAM to be used by the
       application (it begins with a '/'), or a relative pathname from the
       default module location: /lib/security/ or /lib64/security/, depending on
       the architecture.

       module-arguments are a space separated list of tokens that can be used to
       modify the specific behavior of the given PAM. Such arguments will be
       documented for each individual module. Note, if you wish to include
       spaces in an argument, you should surround that argument with square
       brackets.

               squid auth required pam_mysql.so user=passwd_query passwd=mada \
                     db=eminence [query=select user_name from internet_service \
                     where user_name='%u' and password=PASSWORD('%p') and \
                   service='web_proxy']


       When using this convention, you can include `[' characters inside the
       string, and if you wish to include a `]' character inside the string that
       will survive the argument parsing, you should use `\]'. In other words:

               [..[..\]..]    -->   ..[..]..


       Any line in (one of) the configuration file(s), that is not formatted
       correctly, will generally tend (erring on the side of caution) to make
       the authentication process fail. A corresponding error is written to the
       system log files with a call to syslog(3).

       More flexible than the single configuration file is it to configure
       libpam via the contents of the /etc/pam.d/ directory. In this case the
       directory is filled with files each of which has a filename equal to a
       service-name (in lower-case): it is the personal configuration file for
       the named service.

       The syntax of each file in /etc/pam.d/ is similar to that of the
       /etc/pam.conf file and is made up of lines of the following form:

           type  control  module-path  module-arguments


       The only difference being that the service-name is not present. The
       service-name is of course the name of the given configuration file. For
       example, /etc/pam.d/login contains the configuration for the login
       service.

SEE ALSO
       pam(3), PAM(8), pam_start(3)



Linux-PAM Manual                   11/10/2020                        PAM.CONF(5)